Having a For Loop execute 144 times to be sure you get the 144 data points seems perfectly acceptable. The only question I have is how do you know that the first of the 144 data points you collect is actually the first? If the device is sending data continuously without prompting, how do you know it didn't start reading after the first 50 or so data points had been transmitted?
You are using the "Bytes at Port" method which is almost always wrong. What happens if you get 0 bytes? What if you get multiple bytes representing several values? You'll get bad data or you'll wind up missing data.
Why do you have two loops? I don't see anything in the 2nd loop but the waveform graphs that could easily be put in the first loop. I see you have a major race condition problem using a local variable of an indicator to pass data from loop 1 to loop 2. You can easily miss data that way, or wind up reading the same value twice. If you pass data from one loop to another, you should use queues and a producer/consumer design pattern to make sure all the data is passed without loss.
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